Such a device and such a method are known from EP 392 083 and EP 472 825, respectively. The known device comprises a portioning element, which is formed for displacing material from the string of material, so that a reduction in diameter results at this point, said reduction in diameter dividing the string of material into individual sections of a predetermined length, in which said reduction in diameter the twist-off portion for dividing the string of material, for instance into individual sausages, is formed. The portioning element is formed in a manner similar to a flag, i.e. it's one free end is connected to an axis of rotation, whereas the other free end comprises a forming tool for forming a diameter constriction. The portioning element is arranged adjacent to the string of material ejected from a filling machine and moving linearly, wherein the axis of rotation extends perpendicular with respect to the conveying direction of the string of material. The portioning element is driven in a suitable, controlled manner in a way that it moves from a starting position at the predetermined portion into the string of material and after generating the diameter reduction it withdraws from the string of material. The speed of rotation of the portioning element is adapted to the conveying speed of the string of material such that the velocity of circulation of the portioning element when producing the diameter reduction substantially corresponds to the conveying speed of the string of material. If the portioning element has twisted to such an extent that it is withdrawn from the string of material again, it may be provided that the speed of rotation of the portioning element is decelerated or accelerated until reaching the starting position for a new diameter reduction, so that in this manner the length of the sections to be divided can be changed. However, a minimum length is constructively predetermined, which corresponds at least to the distance between the tool and the axis of the portioning element, since the portioning element must always rotate in a manner aligned radially with respect to the axis of rotation. Moreover, the path in which the portioning element may follow the conveying movement of the string of material, is very limited. For sensitive strings of material, for instance strings of material with a coextruded sleeve, which must cure before it can be loaded to a greater extent, this device is less suitable.
A further device for portioning a string of material is known from WO 03/030646, by means of which the string of material shall be dividable variably and synchronously with the rate of extrusion of the string of material. This device includes a portioning element, which is guided on a reciprocating movement path. The drive of the portioning element is formed as a type of connecting rod drive, wherein, however, the drive is carried out via the crankshaft. The crankshaft is driven via a relatively complex gearing and in turn drives a second crankshaft, which is also connected to the portioning element and which takes care that the portioning element basically remains perpendicular with respect to the string of material. It is also described that the drive of the portioning element may have different speeds so that the length of the sections to be portioned can be changed. Caused by the high constructive effort for the transmission, however, a relatively high mass acceleration must be employed, which requires a high drive power.
The common disadvantage of all known portioning devices is, however, their relative limitation to the previously defined operation method.